High frequency switch

ABSTRACT

A switch for conducting or interrupting the flow of current through spaced electrical conductors which introduce a minimum impedance discontinuity and insertion loss when operating in its current-conducting mode. Rapid initiation and termination of current flow is achieved by rapidly displacing a pool of electrically conducting liquid into and out of conducting position, respectively.

United States Patent [72] Inventors Kenneth W. Robbins 2,288,811 7/1942 Leveridge 335/55 Wilmington; 2,296,194 9/1942 Trautman..... 200/152 Gerald F. Ross,Lexington, Mass. 2,303,834 12/1942 Gerisch 200/152 [21] Appl. No. 843,945 2,508,508 5/1950 Garvin 335/55 [22] Filed July 23, 1969 3,141,940 7/1964 Horowitz... 335/52 [45] Patented Mar. 9, 1971 3,363,205 1/1968 Beck 335/52 [73 1 Asslgnee Sperry Rand Corporatio" Primary Examiner- Harold Broome y Attorney-S. C. Yeaton [54] HIGH FREQUENCY SWITCH 4 Claims, 4 Drawing Figs.

[52] U.S.Cl. 335/5,

335/52, 200/152 [5l] Int. `Cl H01h 67/24 ABSTRACT: A Switch for conducting 0,- imemlpting the flow Field ofsealcll 3355,50, of current through spaced electfical conductors which in- 5l,52,55,56; 200/152, 153.18; 333/97(S),7 troduce a minimum impedance discontinuity and insertion loss when operating in its current-conducting mode. Rapid in- [56] References cned itiation and termination of current flow is achieved by rapidly UNITED STATES PATENTS displacing a pool of electrically conducting liquid into and out 2,264,841 12/ 1941 Gallagher 335/56 of conducting position, respectively.

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2 Sheets-Sheet z 21 f INVENTORS KEA/NEM w ROBE/N5 21 55 l BYGERAL-'D F. R055 FIGA. /W

A TTOR/VEY IiiIGlii FREQUENCY SWITCH BACKGROUND OF THE INVENTION l. Field ofthe Invention The invention pertains to means for rapid switching of high frequency signals and more particularly to a switch for the rapid turning on or off of high frequency signals in a transmission line through the use of a plunger element to displace a liquid conductor into and out of a current-conducting relation with spaced conductors which define the transmission line.

2. Description of the Prior Art The prior art teaches many forms of mechanical and electrical switches for interrupting the flow of -electrical currents in high frequency transmission lines, including wave-guiding transmission lines. Certain of these switches of the mechanical type involve the use of sliding elements, mechanical shutters, or the like. They are generally characterized by the use of sliding parts including elements which through wear cause the operation of the switch to deteriorate. Furthermore, the prior art mechanical switches often have built-in losses which are not desirable and present severe impedance discontinuities when placed in a transmission line. While many such switches may be adjusted through the use of impedance-matching elements so as to match the transmission line over a narrow range of frequencies, it has not been possible to operate them over a wide frequency range. For example, in coaxial transmission line, the prior art does not provide a switch suitable for operation as a perfectly matched element over substantially the entire transmission frequency range of the coaxial transmission line.

Other types of transmission line switches include elements made of ferrimagnetic or semiconductor materials which either pass high frequency energy or do not pass it, depending upon external control of the state of the ferrimagnetic or semiconductor elements. Such switches again are characterized by optimum operation only over relatively narrow frequency bands. Furthermore, they are expensive to manufacture and are limited in power handling capability. Both types of switches have in common various defects such as difficulty of adjustment and variation of response with changing frequency and power. Also, prior art structures of both types are complex and expensive to maintain, are undesirably large in size, and are heavy and awkward to operate and maintain.

SUMMARY OF THE INVENTION The invention, in one of its preferred forms, includes first and second aligned electrical conductors with opposed ends forming a gap therebetween. A cylindrical dielectric tubing forms an envelope about the gap and is hermetically sealed adjacent the peripheries of the ends of the conductors. A plunger extending into the end portion of one conductor is preferably adapted to float on a pool of electrically conducting liquid disposed within the opposed end ofthe second conductor. The plunger normally tioats on the pool except when driven by externally applied magnetic field forces, whereupon it forces the liquid against the dielectric tubular envelope to complete an electrical connection between the two opposed ends of the electrical conductors. With the switch in its conducting position, it provides an electrically smooth'conducting path with substantially no impedance discontinuities for the high frequency currents flowing in the transmission line defined by the conductors. Furthermore, the switch of the present invention provides perfect matching and is operative over a wide frequency range.

BRIEF* DESCRIPTION OF THE DRAWINGS inga preferred form ofthe invention used in coaxial line; and

FIG. 4 is a front elevation view partly in section of an alternative form of the switch in its nonconducting position.

DESCRIPTIONI OF THE INVENTION Referring to FIG. 1, there is shown a transmission line of the` single conductor type embodying the inventive transmission line switch. It consists of a first electrical conductor l which may be made of a nonmagnetic material such as stainless steel. Conductor l has a surface coating 20 for providing good high frequency electrical conduction and consisting of a material such as gold, silver, copper, or the like. The device of FIG. 1 includes a second electrical conductor 2 of material similar to that of conductor 1 and similarly supplied with a conductive surface 21. The respective conductors l and 2 are terminated by opposed configured ends 22 and 23 and lie along a common axis to define, in part, a gap region 5.

Gap region 5 is further defined or bounded by a thin tubular dielectric member 7, surrounding gap region S, and extending over the surfaces of conductors 1 and 2 and being sealed thereto. ln one form, therdielectric envelope 7 has an inner wall 42 of diameter substantially equal to the diameters of the coated surfaces 20 and 21 of conductors l and 2, respectively.` In constructing the device, portions of the'coated walls 20 and 2l of the respective conductors 1 and 2 are further coated with a suitable dielectric adhesive. In the assembly of the switch, conductors I and 2 are telescoped into dielectric element 7 so as to form a gap region 5 of desired dimension when the adhesive sets. If desired, the hermetic seal between conductors I and 2 and dielectric member 7 may be made by any of several known methods of bonding a dielectric material, such as glass, to metal surfaces such as those of conductors l and 2.

The respective `ends 22 and 23 of conductors l and 2 are provided with concavities. Referring now particularly to the generally concave region drilled to shape the end 23 of conductor 2, it is relatively shallow and'includes a pool of liquid electrical conductor 25. On the other hand, conductor l has drilled along its axis at end 22 a relatively large cylindrical concavity or hole 24. Mounted within hole 24 is a pistonlike plunger element 30. Plunger element 30 may be constructed at least partly of a relatively light dielectric or insulator material, including such a material as a polymerized fluorocarbon resin material available in the market under the trade name Teflon. Such resins have desirable properties for use in the invention, since they are of relatively low density and can readily be molded to form slidable bearing elements having self-lubricating characteristics.

Plunger element 30 is adapted to slide within hole 24. For this purpose, it is supplied with spaced annular ridges 3l and 32. Ridges 3l and 32 form guides which act substantially to restrain motion of plunger 30 only to translation back or forth within hole 24 along the axis of conductor l, When ridges 3l and 32, like the exterior wall of the plunger element 30, are made of a suitable resin material, ridges or guides 3i and 32 provide permanent lubrication for the slidable plunger to ensure long life for the switch and fast operation.

For enabling plunger element 30 to be moved within hole 24 along the axis of conductor l, a rod 33 of magnetic material is provided within the interior of plunger element 30. Referring to both FIGS. l and 2, rod 33 may be circular in cross section and is inserted in a hole drilled along the axis of plunger element 30. A threaded dielectric retaining screw 50 is provided for holding rod 33 within plunger element 30. Threads 5I provided in an enlarged bore at the top of plunger 33 mate with threads on screw 50 for the purpose of holding and totally enclosing magnetic rod 33 in plunger 30. In an alternative form, magnetic rod 33 is fixed in its axially symmetric position; by using a conventional process for molding the plastic resin plunger shell around it.

Referring to FIG. 1, plunger element 30 has at its lower end an axially symmetric convex conical surface 35. Conical surface 33 generally matches the concave conical shape of the end 23 of conductor 2.

As illustrated in FIG. l, which represents the off or nonconducting configuration of the switch, the plunger element 30 is shown with its conical surface 35 floating on the pool 25 of liquid conductor. It is noted that the specific gravity and other characteristics of the liquid of pool 25 and the mass and other characteristics of the plunger element 30 with its magnetic rod element 33 are appropriately selected so that the rest or unactivated condition of the switch is such that the plunger element 30 is buoyantly supported at its upper position by the liquid. For this purpose, liquid 25 is generally chosen to be mercury, though other liquids may be used, including certain electrically conducting liquids such as metals which are liquid under moderate temperature conditions. Examples of the latter are gallium, cesium, and the like. In the off or nonconducting position ofthe switch, magnetic rod element 33 is not exposed to a controlling or actuating magnetic field. In this condition, the actuating magnetic coil 6 or other source of magnetic field is not excited.

In its preferred form, the invention may employ adjacent the gap end 23 of conductor 2 an annular ridge or lip 40 formed at the periphery of conductor 2. In a further form of the invention, lip 40 may be modified to include a peripheral band 4l. Band 41 may be electrocoated with a material such as silver or gold or other material which tends readily to be wetted, for example, by mercury. As will be explained in the forthcoming discussion of the operation of the invention, elements 430 and 4l, whether they are present singly or in combination afford a desirable meniscus-shaping function and aid the flow of liquid conductor from pool 25 so that a smooth cylindrical conductor surface is formed in gap 5 against dielectric envelope 7 at wall 42. Should conductors l and 2 be made entirely of copper or some other such good electrical conducting material, surfaces of end 23, lip 40, end 22, and hole 24 which come into contact with pool 25 or its vapor are then coated with any suitable material which will not be altered by the liquid of pool 25 if it is, for example, a mercury pool.

The portion of gap region 5 not occupied by the conductive liquid pool 25 and the portion of cavity 24 not occupied by plunger element 30 may be filled during manufacture by any conventional process with a dry inert gas such as nitrogen or one of the noble gases, removal of oxygen and especially of any water vapor present being beneficial in extending the life of the switch. A hole or notch 52 may be provided in each of the annular bearing ridges 31 and 32 to permit the gas to flow back and forth around the plunger element 30 as it is moved up or down, respectively.

The plunger element 30 may be moved downward by ari axial magnetic field generated by electrical currents flowing within a first coaxially mounted coil 6. Coil 6 is supported in any suitable manner around conductor 2 in a plane somewhat below the average position of magnetic rod element 33. Likewise, a second and similar coil 66 may be similarly supported with respect to conductor 1, but in a plane slightly above the average position of magnetic rod element 33.

Reference will not be made to FIGS. l and 2 in discussing the operation of the switch. As noted previously, the switch is illustrated in FIG. l in its open or nonconducting situation. The first coil 6 is not supplied with electrical current. There is no electrical conducting path between the respective surfaces and 2l of conductors 1 and 2. Plunger element 30 is simply floating on the pool 25. Thus, in the quiescent state of the switch, plunger element 30 is located at its upper position by the buoyant forces of the liquid pool 25. Much of the liquid of pool has receded into the cavity formed by the end 23 of conductor 2 and a significant portion of gap region 5 is occupied by inert gas.

FIG. 2 illustrates the situation when the device has been switched to its on or current-conducting position. ln this situation, the magnetic field generating coil 6 is excited by a controlled electrical current flow. Consequently, magnetic forces are exerted on magnetic rod element 33 to pull translatable plunger downward into the cavity 33. A volume of the liquid conductor of pool 25 correspondingto the intruding volume of plunger 30 is displaced in a generally radial and outward direction. As a final result, the liquid conductor of pool 25 moves up into the annular space in gap region 5 not occupied by the lower end of plunger 30. instantaneously, the liquid moves outward over the meniscus-forming elements 40 and 4l, if present, to the internal wall 42 of the envelopedefining dielectric element 7. In the same instant, the liquid firmly contacts the beveled end 22 of conductor l. lt is apparent that the new liquid surface 42 is a smooth and continuous conducting surface identical in dimensional characteristics to the respective surfaces 20 and 2l of conductors l and 2. lt is evident that electrical currents flowing in the transmission line on the surface 20 of conductor 1 and high frequency fields bound to those currents in the region adjacent surface 20 see a continuously smooth transmission line with substantially no impedance change or conductivity change as the currents flow across the surface 42 onto the surface 21 of conductor 2. Since the flow of liquid from pool 25 is substantially equal in all radial directions and the flow is suddenly stimulated by the abrupt translation of plunger element 30 under action of the magnetic field generated by coil 6, the switch changes with great rapidity from its nonconducting to its conducting state, as is desired.

Referring again tov FIGS. I and 2, the switch may be returned from its on or conducting state to its off or nonconducting state simply by removing the excitation current from the magnetic field generator 6. As a consequence, a reversed flow of mercury occurs, returning the state of the elements in the switch from that of FIG. 2 to that of FIG. l. The plunger element 30, no longer being held down by the magnetic field of coil 6, is again forced upward by the influence of gravity on the liquid of pool 25. The liquid of pool 25 flows generally downward and radially into the end cavity 25, flowing away from surface 42 and opening the conducting path at wall 42 with great rapidity. Plunger element 30 is then again buoyantly supported on the pool 25 as in FIG. l and the switch is in condition for recycling.

ln an alternate form of the invention, separate magnetic field generating means may be used to open and close the switch, whereas in the previous illustration, a magnetic field was used only to close the switch, gravity forces being permitted to operi it. For example, it is within the purview of the invention to place a magnetic field generating coil 66 above plunger element 30, as in FIG. 1. In such a construction, coil 6 is energized, as before, to close the switch. To open the switch, coil 6 is deenergized and coil 66 is energized. Coil 66, as noted before, is located in a plane slightly above the average position of magnetic rod element 33. Thus, when an electrical current excites it, magnetic forces on magnetic rod element 33 draw plunger element 30 to its upper position. In this construction, opening of the switch under the influence of gravity on the liquid pool 25 is aided by the magnetic field of coil 66, and the switch is very rapidly opened, Once the switch is open, it may be sustained in that condition by the buoyant action on plunger 30 of liquid pool 25, and current in coil 66 may be turned off in the interest of economical operation. For example, in producing short` pulses of high frequency current flow through the switch from conductor I to conductor 2, coils 6 and 66 are each successively actuated only momentarily, and little magnetizing power is expended in the relatively long dead time between pulses flowing in the transmission line. It is understood that coils 6 and 66 have an internal diameter sufficiently great compared to the diameters of conductors l and 2 that substantially none of the traveling electromagnetic field in the space immediately surrounding conductors l and 2 is intercepted. Alternatively, conductors l and 2 may be coated with a layer of dielectric material more closely to bind the traveling electromagnetic wave to them.

FIG. 3 represents a preferred form of the invention when employed in a coaxial transmission line. The switch is illustrated in this construction in its closed or current-conducting position. Therefore, FIG. 3 can be considered to be analogous to FIG. i. The switch is again disposed in a gap region 5 between opposed ends 22 and 23 of respective conductors ll and 2. The structure of the switch is generally the same as the switch structure taught in FIGS. E. and 2 and corresponding reference numerals have been used to identify corresponding parts of the structure. its operation is also the same in FlG. 3 as has been taught in connection with FIGS. l and 2.

Referring to FiG. 3, there is shown a transmission line having structural elements similar to those of FlGS. ll and 2 to which have been added the elements required to operate the switch in a conventional coaxial transmission system. In FIG. 3, first and second electrical conductors ll and 2 have respective opposed ends 22 and 23 forming a gap region 5 therebetween. A cylindrical dielectric tubing 7 forms an envelope about the gap region 5 and is hermetically sealed adjacent the peripheries ofthe respective ends 22 and 23 of conductors ll and 2. A plunger element 30 extending into the end portion of a first conductorl is adapted to float on a pool of electrically conducting liquid 25 disposed in the opposed end of conductor 22,

Conductor l, conductor 2, and the previously described switching elements within gap region 5 are supported as is common practice in coaxial transmission line practice by perforated dielectric disc spacers I and ll fixed within an outer conducting tube l5. In the region of conductor I, for example, conductor ll, conducting tube l5, and dielectric supporting disc spacer i@ form a conventional coaxial line. The outer wall of conducting tube l may directly support a coil 6 for actuation of the plunger element in gap region 5. The location and function of coils 6 and 66 in FIG. 3 with respect to plunger element 30 are similar to those in FIGS. l and 2.

Referring again to FIG. 3, apertures I6 and 17 in dielectric supporting discs lll) and lll may respectively be supplied in disc spacers l0 and ll for the purpose of permitting evacua- Vtion or pressurizing of the coaxial transmission line in the conyentional manner. Furthermore, should it be found that there is any slight impedance mismatch present because of the presence of the thin dielectric tube 7, well known impedance matching means represented by the increased inner diameter of conducting tube l5 in the region I8 may be employed.

In the operation of the switch of FIG. 3, the absence of mercury at the wall 452 forming a smooth continuing surface between surfaces 2f) and 2i produces, with the cooperation of tubular conductor l5, a hollow wave guide below cutoff region in the interior of the transmission line, having a well 'known incapability of supporting energy transmission, When plunger element 30 is pulled downward by the magnetic field generated by coil 6, a smooth, continuous conducting path is provided between surfaces and 2l, and the transmission line again supports energy transmission.

A further embodiment of the switch mechanism of the invention is shown in FIG. 4, wherein reference numerals corresponding to those used in preceding F lGS. are used to `identify corresponding parts. Referring to FIG. 4i, there is shown a modification of the invention that again includes first and second electrical conductors l; and 2. Conductors l and 2 may again be constructed of stainless steel and may be supplied with respective coatings 20 and 21 of good high frequeney electrically conductive material. The respective conductors l and 2 are terminated by opposed configured ends 22 and 23, lie along a common axis, and define a modified gap region 75.

Gap region 75 is in part bounded by a thin tube of glass 7 or of other dielectric material, extending over the surfaces of :onductors i and 2. In this embodiment, the dielectric member 7 has a slightly smaller inner diameter than the diameter of conductors i and 2 for purposesthat will become apparent. ln constructing the device, the dielectric member 7 s slid over a reduced diameter portion 76 of conductor li and :hen the conductor 2, also having a similar reduced portion 77, is inserted within the opposite end of dielectric element 7. Arnnular rings 79 of a suitable sealant such as epoxy cement ire applied to fix conductor l within the upper end of dielectric element 7 and to fix conductor 2 within its lower end.

The respective ends 22 and 23 of conductors ll and 2 are again provided with concavities, but of modified shape with respect to those of the preceding FIGS. As will become apparent, this is done for the purpose of supporting both the plunger element and the electrically conductive liquid pool in cooperative relationship within an end of only one of the conductors. Referring now particularly to the generally concave region or hole 78 drilled in the end 23 of conductor 2, it is relatively deep and includes a pool of liquid electrical conductor 85. rfoward the gap region 75, the diameter of hole 78 is increased to form a relatively enlarged bore' 86. The depth of bore 86 is relatively small compared to the depth of the hole Mounted within hole 78` is a pistonlike plunger element 80. Plunger element 80 may again be constructed at least partly of .a lightweight insulator material such as any moldable material of the types known by the trade names Teflon or nylon. Plunger element 80 is adapted to slide within hole 78. For this purpose, it is supplied with horizontal rows of dimples 82 and 83, respectively, these dimples being formed on the cylindrical surface of plunger element 80 when it is cast by any well known molding process. Dimples 82 and 83 are spaced at 90 intervals and, like the ridges 31 and 32 of F IGS. I and 2, actas bearing elements to restrain 'motion of plunger element 80 so that it is allowed to move only along its axis of symmetry.

, For enabling plunger 80 to be moved within hole 78, a relatively large diameter rod element 87 of magnetic material is placed within an axial bore `88 in plunger 80. Plunger 80 has an upper end in the shape of an upwardly expanding truncated cone 90, the purpose of which will be apparent in the discussion to follow of the operation of the embodiment of the switch. To retain the magnetic rod 87 in place and `to ensure that plunger element 80 is hermetically sealed, a thin circular disc 89 is fastened to the top of the conical portion 90 of plunger 80 by any suitable adhesive, such as those known as epoxy cements. i

FIG. 4 represents the off or nonconducting configuration of the switch, the vertical and` bottom walls of plunger element 80 being shown substantially totally immersed within and buoyantly supported by a pool of an electrically conducting liquid such as mercury. ln the rest or nonconducting condition of the switch, the pool occupies the regions of the bores 78 and 86 common to the gap region 75, to the conical wall 90, to the cylindrical wall 91 of plunger 80, and to its flat lower surface 92. As in FIGS. I and 2, the specific gravity and other characteristics of the liquid of pool 85 and the mass and other characteristics of plunger element 80 are designed so that the i rest or unactivated condition of the switch holds plunger element in a stable buoyantly supported condition. For this purpose, because the liquid pool 85 is generally chosen to be mercury, a relatively large and heavy magnetic rod element 87 is employed.

As in FlGS. i and 2, the invention of FIG. 4 may employ adjacent gap end 23 of conductor 2 an annular lip 40 formed at the periphery of conductor 2 and may include a peripheral band 4I plated with a material which tends to be wetted by mercury, Elements 4@ and 4l, as explained previously, have the function of desirably shaping the meniscus 43 of the liquid of pool 85 in the gap region 7S. The portion of gap region 75 not occupied by mercury may be supplied with a dry inert gas.

Now, referring particularly to the end 22 of conductor l, it has a flat horizontal surface 93, since it must no longer be specially shaped to accommodate a plunger element. lts periphery is supplied with a beveled end or lip 22 which, like annular lip 451i of end 23, may be coated with a'material wetted by mercury.

The plunger element 30 is moved downward by an axial magnetic field produced by electric currents flowing within a coaxially mounted magnetic field generator or coil 96. Coil 96 is supported below the average position of magnetic rod element 87.

Operation of the switch will be generally understood by reference to the discussion of the operation of the embodi merit shown in FIGS. l and 2. However, referring particularly to FIG. 4 which, as noted above, shows the nonconducting configuration of the switch, magnetic field generating coil 96 is not excited and the top of the mercury pool 85 lies in the plane substantially coincident with the lower edge of the nylon disc 89 fastened at the top of plunger 80. A mercury meniscus is formed at the outer edge of the mercury pool where it is seen that the mercury surface curves toward the upper end of lip 4l. A nonconductive discontinuity is clearly formed between said upper mercury surface and the lip 22 on the periphery of conductor 1.

When it is desired to permit current flow through the inventive transmission line switch, switch 101 is closed, permitting direct current to flow from battery E through coil 96 and generating a magnetic field along the axis of symmetry of the transmission line. Because of the indicated placement of coil 96 relative to the average position of plunger element 80, the latter is abruptly forced downward. The mercury of pool 85 is shoved outward and upward due to the downward axial motion of plunger 80 and the shape or slope of cone 90. The level of pool 85 instantaneously rises and the mercury comes into intimate contact with lip 22. lt is also forced into intimate contact with the inner wall 42 of dielectric element 7. lt is apparent that the liquid surface at wall 42 is a smooth and continuous conducting surface between the ends of conductors 1 and 2. First, it is a smooth electrical conducting surface because it is a geometrically smooth physical continuation of the end of conductor l into the end of conductor 2. The continuity of the conducting surface is electrically perfect over a broad band, the dielectric element 7 having been slightly recessed at areas 76 and 77 with respect to the full diameters of conductors l and 2, forming in the well-known manner a smooth impedance matching element over a broad band at the region encompassed by dielectric element 7.

As in FIGS. l and 2, the transmission line switch may be returned from its on or conducting state to its nonconducting state simply by opening switch 10i and thus removing the excitation current from coil 96. As a consequence, a reversed flow of mercury occurs, again opening the portion of the gap region 75 between lips 22 and 40 and ending the flow of high frequency current between conductors l and 2. The plunger element 80, no longer being held down by the magnetic field, is again forced up to the position illustrated in F IG. 4 by the influence of gravity on the liquid pool 85. Element 80 is then again buoyantly supported on the pool 85 and the transmission line switch is in condition for recycling.

While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes may be made without departing from the true scope and spirit of the invention in its broader aspects.

We claim:

l. ln apparatus for use with a transmission line:

first and second electrical conductors having respective first and second ends with a space therebetween;

dielectric means connecting said conductors and completing an envelope about said space, said dielectric means forming a hermetic seal with each of said conductors;

a pool of mercury disposed within at least a portion of said space and adapted to conduct electricity; at least one of said conductor ends having a surface adjacent said dielectric means with a' surface material capable of forming an amalgam with said mercury; plunger means movable in said space for displacing said mercury thereby to provide an electrical path between said first and second conductors; said plunger means being adapted to displace said mercury for urging it into intimate contact with at least the peripheral portions of each of said ends, and said plunger means comprising a dielectric element including a magnetic armature and adapted to be buoyantly supported by said mercury; hollow electrical conductor means aligned coaxially with respect to said first and second conductors and forming therewith a coaxial transmission line; and

magnetic field generating means cooperating with said magnetic armature for moving said plunger, said magnetic field generating means coaxially surrounding said hollow electrical conductor means.

2. In apparatus for use in a transmission line:

first and second electrical conductor means having respective first and second high frequency current conducting surfaces and respective first and second ends with a space therebetween;

dielectric means connecting said high frequency current conducting surfaces in hermetically sealed relation thereto for completing an envelope about said space,

said dielectric means having an inner surface forming a substantially direct continuation o f said first surface into said second surface;

a pool of electrically conductive liquid disposed within said space, l said liquid having surface characteristics adapted for conducting high frequency currents; plunger means movable in said space for displacing said liquid thereby to complete a continuous high frequency current conducting path along said first surface, along said liquid surface where contacting said inner surface of said dielectric means, and along said third surface; and

said first surface, said liquid surface, and said third surface being so constructed and arranged as to conduct said high frequency currents therealong with substantially no reflection of said high frequency currents.

3. Apparatus as described in claim 2 wherein:

said first and second high frequency current conducting surfaces form circular cylinders having respective first and second diameters; and

said inner surface of said dielectric means is circularly cylindric and has a diameter substantially equal to said first and second diameters.

4. ln apparatus of the character recited in claim 2, wherein at least one of said electrical conductor means has a surface adjacent said inner surface of said dielectric means coated with a material capable of being wetted by said liquid for providing fast formation of said high frequency conducting path, thereby affording fast rise initiation of high frequency current flow along said tirst and second surfaces with substantially no current reflection. 

1. In apparatus for use with a transmission line: first and second electrical conductors having respective first and second ends with a space therebetween; dielectric means connecting said conductors and completing an envelope about said space, said dielectric means forming a hermetic seal with each of said conductors; a pool of mercury disposed within at least a portion of said space and adapted to conduct electricity; at least one of said conductor ends having a surface adjacent said dielectric means with a surface material capable of forming an amalgam with said mercury; plunger means movable in said space for displacing said mercury thereby to provide an electrical path between said first and second conductors; said plunger means being adapted to displace said mercury for urging it into intimate contact with at least the peripheral portions of each of said ends, and said plunger means comprising a dielectric element including a magnetic armature and adapted to be buoyantly supported by said mercury; hollow electrical conductor means aligned coaxially with respect to said first and second conductors and forming therewith a coaxial transmission line; and magnetic field generating means cooperating with said magnetic armature for moving said plunger, said magnetic field generating means coaxially surrounding said hollow electrical conductor means.
 2. In apparatus for use in a transmission line: first and second electrical conductor means having respective first and second high frequency current conducting surfaces and respective first and second ends with a space therebetween; dielectric means connecting said high frequency current conducting surfaces in hermetically sealed relation thereto for completing an envelope about said space, said dielectric means having an inner surface forming a substantially direct continuation of said first surface into said second surface; a pool of electrically conductive liquid disposed within said space, said liquid having surface characteristics adapted for conducting high frequency currents; plunger means movable in said space for displacing said liquid thereby to complete a continuous high frequency current conducting path along said first surface, along said liquid surface where contacting said inner surface of said dielectric means, and along said third surface; and said first surface, said liquid surface, and said third surface being so constructed and arranged as to conduct said high frequency currents therealong with substantially no reflection of said high frequency currents.
 3. Apparatus as described in claim 2 wherein: said first and second high frequency current conducting surfaces form circular cylinders having respective first and second diameters; and said inner surface of said dielectric means is circularly cylindric and has a diameter substantially equal to said first and second diameters.
 4. In apparatus of the character recited in claim 2, wherein at least one of said electrical conductor means has a surface adjacent said inner surface of said dielectric means coated with a material capable of being wetted by said liquid for providing fast formation of said high frequency conducting path, thereby affording fast rise initiation of high frequency current flow along said first and second surfaces with substantially no current reflection. 